What is exploration?
The purpose of exploration is to locate areas where mineral and petroleum resources may be present, to establish the quality and quantity of those resources, and to investigate the viability of extracting the resource.
Before exploring for minerals or petroleum in NSW, an explorer must be granted an Exploration Licence (EL) or an Assessment Lease (AL) under the Mining Act 1992 or a Petroleum Exploration Licence (PEL) or an Petroleum Assessment Lease (PAL) under the Petroleum (Onshore) Act 1991 by the Department of Regional NSW.
Before a prospecting title holder can access land for exploration, a written land access arrangement must be in place between the landholder and the title holder.
Types of exploration activities
There are a range of activities that may be undertaken as part of an exploration program. These activities depend on a number of factors, including the nature of the mineral being sought and the geology of the area. Exploration generally starts with low impact activities to determine whether signs of minerals or petroleum are evident before progressing to more intense and costly activities like drilling and bulk sampling.
Geological mapping is undertaken by walking over the ground of interest. Geologists observe the location, orientation and characteristics of rocks or sediments exposed at the surface. This information is used to prepare a geological map of the area, recording the rock types and structures.
Geochemical surveys are generally undertaken to target areas for further exploration. The surveys usually involve collecting samples of soils, rocks and/or sediments. These samples undergo chemical analysis at a laboratory.
Soil and subsoil sampling is usually undertaken using hand-held tools such as shovels, picks and hand augers. Samples are usually collected in a grid pattern and involve collecting small (approximately one kg) samples of soil. Holes excavated during the program are usually back-filled immediately following sampling.
Geophysical surveys assist in mapping different rock types and can help identify resources without the need for direct observation. Different geophysical surveys measure various physical properties of Earth, and have different applications and equipment. Geophysical surveys can be conducted from the air, at surface, and down drillholes. They include:
Airborne geophysical surveys may comprise magnetic, radiometric, gravity or electromagnetic surveys. These surveys provide general geological information for an area and are often used in the initial stages of exploration. They are typically undertaken using low-flying helicopters or aircraft which fly in a grid pattern. The instruments may be either mounted on or towed beneath the aircraft. Depending on the type of survey, the aircraft may fly between 25 m and 60 m above the ground, with flight lines spaced between 25 m and 200 m apart.
Seismic surveys measure variations in reflected ground vibrations as they pass through the earth. The surveys use an energy source to create the high frequency vibrations, which can be truck-mounted vibrating weights or a simple hammer hit depending on the scale of the survey. Small sensors are linked by cables and spread either side of the source to detect and relay the vibrations as they return to the surface. Seismic surveys provide information about rocks down to depths of several kilometres and are particularly suited to flat-lying sedimentary basins. They are most often used in petroleum and coal exploration.
Magnetic surveys measure the variations of Earth's magnetic field due to the presence of magnetic minerals. Subtle variations in the abundance of magnetic minerals are used to interpret rock types and can assist in identifying resources.
These surveys are typically undertaken by a geophysical technician on foot carrying a magnetometer and a sensor on a pole. They are most often used in metallic mineral exploration.
Radiometric surveys measure gamma rays which are continuously being emitted from Earth by natural decomposition of some common radiogenic minerals.
The surveys focus on recording the naturally occurring radiation from potassium, thorium and uranium. Generally most gamma rays emanate from the top 30 cm of rock or soil and can detected by airborne surveys or on surface rocks using a hand-held spectrometer. They are most often used in metallic and industrial mineral exploration.
The gravity field is measured with a gravimeter to determine variations in rock density in the Earth's crust. Ground gravity surveys require a geophysical technician to take gravity measurements at set intervals of distance and record the precise height at each location. Access to the recording sites can be by vehicle or helicopter, depending upon remoteness. They are used in mineral and energy exploration.
Induced Polarisation surveys
Induced Polarisation surveys induce an electric field in the ground and measure the chargeability and resistivity of the subsurface. The technique can identify differences in resistivity arising from aquifers, metallic minerals and stratigraphy. Readings are taken by a small crew who shift a ground array of transmission and receiver cables. They are most often used in metallic mineral exploration.
Electromagnetic surveys induce an electromagnetic field and measure the 3 dimensional variations in conductivity within the near-surface soil and rock. Conductive units can be studied to locate metallic minerals, and to understand groundwater and salinity. Ground readings are taken by a small crew who shift a ground array of transmission and receiver cables. They are most often used in metallic mineral exploration.
Drilling is often conducted as part of an exploration program to obtain detailed information about the rocks below the ground surface. The drilling method used depends on the type of rocks and information sought. The degree of disturbance around the drillhole varies with each method, however, strict environmental safeguards ensure all drill sites are rehabilitated after the completion of drilling.
Auger drilling – This method uses either a hand-held power auger or one mounted on a small vehicle. It is similar to a post-hole digger used by farmers when fencing.
Air drilling – There are 2 main shallow air drilling methods: aircore and rotary air blast. These methods usually involve a utility or small truck-mounted rig with an air compressor carried onboard or towed separately. This type of drilling creates rock fragments (chips). These are removed from the drillhole by compressed air, which is forced down the drillhole and lifts the rock chips to the surface. This type of drilling requires minimal site preparation and rehabilitation.
Air drilling – There are 2 main types of air drilling used to drill deeper holes: open-hole percussion and reverse circulation. These methods usually involve truck mounted rigs with one or 2 support vehicles to carry drill rods and air compressor capacity. These drilling techniques produce rock chips that are lifted to the surface by compressed air and do not necessarily require significant site preparation and rehabilitation.
Diamond drilling – A truck-mounted rig with support vehicles is used to extract a continuous cylinder of rock. Diamond drilling uses water and drilling fluids that are contained in either an in-ground sump or above-ground tanks, and requires significant site preparation and rehabilitation. Most exploration for coal and minerals uses a combination of diamond and reverse circulation drilling.
Rotary mud drilling – Rotary mud drilling is most often used for petroleum and deep stratigraphic drilling. This method produces fine rock fragments and uses water and drilling fluids to lubricate the drill bit and return the rock fragments to the surface. The drilling fluids are contained in either in-ground sumps or above-ground tanks. The drilling rigs are usually larger than for other methods and require more support vehicles and site preparation.
Bulk sampling operations
Prior to applying to develop a mine, an explorer may extract a bulk sample of the material to be mined to allow further testing and refinement of the proposed mining procedures. Extraction of a bulk sample in NSW requires approval from Department of Regional NSW. Large samples may also require approval from the Department of Planning and Environment.